Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$108.77	3.412%	$112.4812	$112.48	$112.50	$112.50
Purchase #2	$231.59	13.628%	$263.1511	$263.15	$263.15	$263.20
Purchase #3	$65.43	12.714%	$73.7488	$73.75	$73.75	$73.70
Purchase #4	$6.67	5.833%	$7.0591	$7.06	$7.05	$7.10
Purchase #5	$20.82	5.571%	$21.9799	$21.98	$22.00	$22.00
Purchase #6	$18.28	13.345%	$20.7195	$20.72	$20.70	$20.70
Purchase #7	$69.37	12.514%	$78.051	$78.05	$78.05	$78.10
7 purchase totals =	$520.93		$577.1906	$577.19	$577.20	$577.30